The present invention relates to a process for operating a piston engine and a piston engine, in particular for a motor vehicle.
DE 198 19 937 C1 discloses an operating process for an electronic engine control system of a piston engine. The engine control system determines a current exhaust gas mass proportion from a current fuel/air mass ratio of a fresh gas supplied to a combustion chamber of the piston engine and from a current fuel/air mass ratio of an exhaust gas carried away from the combustion chamber after the combustion. The current exhaust gas mass proportion forms the contents of the combustion chamber together with a fresh gas mass proportion after the fresh gas has been supplied and before combustion.
It is of particular interest to know the exhaust gas mass proportion, which can also be referred to as the “residual gas proportion”, as accurately as possible if the operating behavior of the piston engine is to be optimized, particularly with regard to fuel consumption, emission of pollutants and the efficiency of the engine. Modern internal combustion engines (for example petrol engines with direct fuel injection, diesel engines with direct fuel injection, diesel engines with common rail fuel injection) may be equipped with an exhaust gas recirculation device in order to reduce the emissions of pollutants and the fuel consumption. Here, part of the combustion output is returned to the combustion stage through a corresponding return line leading from the exhaust tract to the fresh air supply tract. In the process, such an external exhaust gas recirculation system changes the fuel/air mass ratio of the mixture introduced into the particular cylinder and therefore has a significant influence on the combustion process taking place there. In addition, this also changes the composition of the exhaust gases, the power output and the smooth running of the piston engine.
In addition to this external exhaust gas recirculation, the operating behavior of the piston engine is also influenced by internal exhaust gas recirculation which is formed, for example, by a dead volume which cannot be displaced from the associated cylinder by a piston. Furthermore, during the charging of the mixture into the cylinder, there is also an overlapping of the closing motion of the exhaust valve or valves and the opening motion of the intake valve or valves, which overlapping causes exhaust gases to flow back, the latter having already been displaced from the cylinder into the exhaust tract.
With the aid of the known engine control system, the contents of the cylinders, which contents are formed from the supply of a fresh fuel/air mixture, the external exhaust gas recirculation and the internal exhaust gas recirculation, can be determined relatively precisely, so that, with the aid of a suitable open or closed loop control system, the operating behavior of the piston engine can be influenced as a function of the contents of the cylinders.